diff options
Diffstat (limited to 'Documentation/filesystems/caching')
| -rw-r--r-- | Documentation/filesystems/caching/netfs-api.txt | 73 |
1 files changed, 60 insertions, 13 deletions
diff --git a/Documentation/filesystems/caching/netfs-api.txt b/Documentation/filesystems/caching/netfs-api.txt index 11a0a40ce445..aed6b94160b1 100644 --- a/Documentation/filesystems/caching/netfs-api.txt +++ b/Documentation/filesystems/caching/netfs-api.txt @@ -29,15 +29,16 @@ This document contains the following sections: (6) Index registration (7) Data file registration (8) Miscellaneous object registration - (9) Setting the data file size + (9) Setting the data file size (10) Page alloc/read/write (11) Page uncaching (12) Index and data file consistency - (13) Miscellaneous cookie operations - (14) Cookie unregistration - (15) Index invalidation - (16) Data file invalidation - (17) FS-Cache specific page flags. + (13) Cookie enablement + (14) Miscellaneous cookie operations + (15) Cookie unregistration + (16) Index invalidation + (17) Data file invalidation + (18) FS-Cache specific page flags. ============================= @@ -334,7 +335,8 @@ the path to the file: struct fscache_cookie * fscache_acquire_cookie(struct fscache_cookie *parent, const struct fscache_object_def *def, - void *netfs_data); + void *netfs_data, + bool enable); This function creates an index entry in the index represented by parent, filling in the index entry by calling the operations pointed to by def. @@ -350,6 +352,10 @@ object needs to be created somewhere down the hierarchy. Furthermore, an index may be created in several different caches independently at different times. This is all handled transparently, and the netfs doesn't see any of it. +A cookie will be created in the disabled state if enabled is false. A cookie +must be enabled to do anything with it. A disabled cookie can be enabled by +calling fscache_enable_cookie() (see below). + For example, with AFS, a cell would be added to the primary index. This index entry would have a dependent inode containing a volume location index for the volume mappings within this cell: @@ -357,7 +363,7 @@ volume mappings within this cell: cell->cache = fscache_acquire_cookie(afs_cache_netfs.primary_index, &afs_cell_cache_index_def, - cell); + cell, true); Then when a volume location was accessed, it would be entered into the cell's index and an inode would be allocated that acts as a volume type and hash chain @@ -366,7 +372,7 @@ combination: vlocation->cache = fscache_acquire_cookie(cell->cache, &afs_vlocation_cache_index_def, - vlocation); + vlocation, true); And then a particular flavour of volume (R/O for example) could be added to that index, creating another index for vnodes (AFS inode equivalents): @@ -374,7 +380,7 @@ that index, creating another index for vnodes (AFS inode equivalents): volume->cache = fscache_acquire_cookie(vlocation->cache, &afs_volume_cache_index_def, - volume); + volume, true); ====================== @@ -388,7 +394,7 @@ the object definition should be something other than index type. vnode->cache = fscache_acquire_cookie(volume->cache, &afs_vnode_cache_object_def, - vnode); + vnode, true); ================================= @@ -404,7 +410,7 @@ it would be some other type of object such as a data file. xattr->cache = fscache_acquire_cookie(vnode->cache, &afs_xattr_cache_object_def, - xattr); + xattr, true); Miscellaneous objects might be used to store extended attributes or directory entries for example. @@ -733,6 +739,47 @@ Note that partial updates may happen automatically at other times, such as when data blocks are added to a data file object. +================= +COOKIE ENABLEMENT +================= + +Cookies exist in one of two states: enabled and disabled. If a cookie is +disabled, it ignores all attempts to acquire child cookies; check, update or +invalidate its state; allocate, read or write backing pages - though it is +still possible to uncache pages and relinquish the cookie. + +The initial enablement state is set by fscache_acquire_cookie(), but the cookie +can be enabled or disabled later. To disable a cookie, call: + + void fscache_disable_cookie(struct fscache_cookie *cookie, + bool invalidate); + +If the cookie is not already disabled, this locks the cookie against other +enable and disable ops, marks the cookie as being disabled, discards or +invalidates any backing objects and waits for cessation of activity on any +associated object before unlocking the cookie. + +All possible failures are handled internally. The caller should consider +calling fscache_uncache_all_inode_pages() afterwards to make sure all page +markings are cleared up. + +Cookies can be enabled or reenabled with: + + void fscache_enable_cookie(struct fscache_cookie *cookie, + bool (*can_enable)(void *data), + void *data) + +If the cookie is not already enabled, this locks the cookie against other +enable and disable ops, invokes can_enable() and, if the cookie is not an index +cookie, will begin the procedure of acquiring backing objects. + +The optional can_enable() function is passed the data argument and returns a +ruling as to whether or not enablement should actually be permitted to begin. + +All possible failures are handled internally. The cookie will only be marked +as enabled if provisional backing objects are allocated. + + =============================== MISCELLANEOUS COOKIE OPERATIONS =============================== @@ -778,7 +825,7 @@ COOKIE UNREGISTRATION To get rid of a cookie, this function should be called. void fscache_relinquish_cookie(struct fscache_cookie *cookie, - int retire); + bool retire); If retire is non-zero, then the object will be marked for recycling, and all copies of it will be removed from all active caches in which it is present. |